Energy Spectra Variations of Energetic Ions Associated With a Stream Interaction Region

Abstract

AbstractUnderstanding the evolution of energetic particles in the heliosphere is one of the most outstanding topics in heliophysics studies. The spectra of energetic particles are pivotal to investigate their origin, acceleration and transport processes. Using STEREO A data, we investigate an intensity enhancement of energetic ions associated with a stream interaction region (SIR) during the decay phase of a gradual solar energetic particle (SEP) event. We find the SIR has fine structures include the stream interface (SI) and a forward‐reverse shock pair, and the energy spectra of energetic ion intensities show complex variations around them. Furthermore, we compare the ions' energy spectra in different regions of the SIR. The results show that this SIR is capable of accelerating protons to about 35 MeV nuc−1, which is about two times of the upper limit of the energy as identified by previous observations, but they are still of the same order. We suggest this may be explained by the fact that the SIR could further accelerate the remnant lower energy ions from the gradual SEP event to higher energies. Moreover, the energetic ions in the SIR event have two populations that are accelerated by shock‐associated and non‐shock‐associated mechanisms, respectively. In addition, the ion intensity exhibits significant directional anisotropies during this SIR event, which may be a result of the combined influence of the transport effect, shock, and the intervening small flux rope.